Forum Schedule Spring 2026

This talk will focus on experimental and theoretical research into nonlinear molecular rovibrational spectroscopy. One focus will be on the spectroscopy of CH4 where a high power single mode OPO is used to pump individual transitions in the n3 fundamental and the resulting disequilibrium probed with near IR radiation from a either a frequency comb or a single mode cw laser. This has allowed us to probe transitions to states with ~9000 cm-1 of vibrational energy with resolution of ~1-10 MHz and frequency accuracy of ~10 kHz. We have used a modification to measure dipole moments of the E symmetry states in his region. The other focus will be on degenerate, Doppler free, two-photon transitions detected using a version of Cavity Ring-down Spectroscopy. This increases spectral resolution by about two orders of magnitude and reduces effective line density also by a few order of magnitude due to the selectivity for transitions that are nearly double resonant. In favorable cases, the sensitivity is even higher than for detection using single photon transitions of the same molecule.

The X-ray spectra of accreting supermassive black holes encode the physics of the innermost regions: the accretion disk, the broad-line region, and powerful outflows. However, two decades of CCD-resolution observations left these components blended and ambiguous. The Fe Kα emission line at 6.4 keV is the single most powerful diagnostic of this environment: produced by fluorescence when hard X-rays irradiate circumnuclear matter, its profile encodes the location, kinematics, and physical conditions of the emitting gas, from the inner accretion disk to the broad-line region to the molecular torus. XRISM/Resolve, the first X-ray microcalorimeter to observe a large sample of active galactic nuclei, changes the game: its 5 eV energy resolution in the Fe K band (resolving power of ~1300 at 6 keV) cleanly separates narrow core, broad, and Compton-shoulder components for the first time. I present an overview of the early XRISM observations of active galactic nuclei, showing how Resolve's ability to decompose the Fe K complex into its distinct physical components builds a coherent picture of the circumnuclear environment that connects, for the first time, to what we know from optical, UV, and infrared observations. I discuss constraints on ultra-fast outflows, the view into Compton-thick nuclei, and the questions this new spectral clarity opens for the future of high-resolution X-ray astrophysics.